An untested node-port of https://github.com/foertel/pihp

gistfile1.js

var Gpio = require('onoff').Gpio,
    async = require('async'),
    _ = require('underscore');

var measureDistance = function(opts) {
    var options = _.defaults(opts, {
        trigger: 24,
        echo: 25,
        leds: [4, 17, 18, 27, 22, 23],
        timeout: 2000
    }),

    distances = [],
    triggerGpio,
    echoGpio,
    ledsGpio,

    getDistance = function(cb) {
        var start, to;

        var run = function() {
            to = setTimeout(function() {
                echoGpio.unwatchAll();
                cb(new Error('timeout reached'));
            }, options.timeout);
    
            echoGpio.watch(function(val) {
                if (val) {
                    start = Date.now();
                } else {
                    clearTimeout(to);
                    echoGpio.unwatchAll();
                    cb(null, (Date.now() - start) * 34300 / 2);
                }
            });
        };
        
        triggerGpio.write(1, function() {
            setTimeout(_.partial(_.bind(triggerGpio.write, triggerGpio), 0, run), 1);
        });
        
    },

    getAverageDistance = function() {
        var len = distances.length;

        distances.sort(function(a, b) {
            if (a > b) return 1;
            if (b > a) return -1;
            return 0;
        });

        distances = distances.slice(Math.round(len * 0.25), Math.round(len * 0.5));

        return _.reduce(distances, function(distance, memo) {
            return distance + memo;
        }, 0) / len;
    },

    switchLeds = function() {
        var ledsToSwitch = Math.floor(getAverageDistance() / 10);

        _.each(ledsGpio, function(ledGpio, idx) {
            ledGpio.writeSync(idx < ledsToSwitch ? 1 : 0);
        });
    };

    return {

        start: function() {
            distances = [];
            triggerGpio = new Gpio(options.trigger, 'out');
            echoGpio = new Gpio(options.echo, 'in');
            ledsGpio = _.map(this.options.leds, function(pin) {
                return new Gpio(pin, 'out');
            });

            async.forever(function(next) {
                getDistance(function(err, distance) {
                    if (err) {
                        return next();
                    }

                    distances.push(distance);

                    if (distances.length > 30) {
                        switchLeds();
                    }
                    
                    next();
                });
            });
        },

        stop: function() {
            triggerGpio.unexport();
            echoGpio.unexport();
            _.each(ledsGpio, function(ledGpio) {
                ledGpio.unexport();
            });
        }

    };
};

var dist = measureDistance();

// Boot the whole thing
dist.start();

process.on('SIGINT', function() {
    dist.stop();
    process.exit();
});